1. Field of the Invention
The present invention relates to a polymerizing apparatus for polymerizing a monomer having an ethylenically unsaturated double bond wherein a reaction mixture is polymerized while it is circulated through a heat exchanger installed separately from a polymerization vessel.
2. Description of the Prior Art
The polymerization reaction of a monomer having an ethylenically unsaturated double bond is carried out in such a manner that a polymerization medium such as water, a monomer having an ethylenically unsaturated double bond, a polymerization initiator, a dispersant, and, if required, other various additives are charged into a polymerization vessel equipped with a jacket and a reflux condenser, and then the reaction is initiated by elevating the temperature in the polymerization vessel to a prescribed temperature. Further, during the polymerization reaction, in order to retain the reaction system at a prescribed temperature, the heat of polymerization reaction is removed by passing cooling water through the jacket and the reflux condenser.
In recent years, in order to improve the productivity, measures are adopted that (1) the polymerization vessel is made large in size and (2) the polymerization time per batch is shortened. However, since the enlargement of the polymerization vessel has resulted in a decrease in the ratio of the heat transfer area to the reaction mixture, the above prior technique of removing the heat of polymerization reaction has become insufficient in capacity for removing the heat. In addition, if the polymerization time per batch is shortened, the capacity for removing the heat becomes insufficient further because the rate of the generation of heat due to the polymerization reaction per unit time increases.
Some techniques for overcoming the above disadvantages are suggested and, as effective techniques out of them, techniques wherein a reaction mixture is circulated through a heat exchanger installed outside a polymerization vessel (see Japanese Pre-examination Patent Publication (kokai) Nos. 54-24991 (1979), 56-47410 (1981), and 58-32606 (1983) and Japanese Patent Publication (kokoku) No. 64-11642 (1989)) can be mentioned. These techniques are quite effective in that the ratio of the heat transfer area to the reaction mixture can be increased.
However, according to these techniques, since the reaction mixture in the form of a slurry came back from the heat exchanger scatters when the reaction mixture is discharged into the gaseous phase part in the polymerization vessel from a return nozzle of a circulating pipeline, there is a problem that a large amount of scale of a polymer deposits on the gaseous phase part and near to the interface between the gaseous phase part and the liquid phase part in the polymerization vessel. Further, there is a problem that when the obtained polymer is worked into a molded product such as a sheet, fish eyes increases.